1. Field of the Invention
The present invention relates to new polymers and use of such polymers as a resin binder component for photoresist compositions, particularly chemically-amplified positive-acting resists that can be effectively imaged at short wavelengths such as sub-200 nm, particularly 193 nm.
2. Background
Photoresists are photosensitive films used for transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist-coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.
A photoresist can be either positive-acting or negative-acting. For most negative-acting photoresists, those coating layer portions that are exposed to activating radiation polymerize or crosslink in a reaction between a photoactive compound and polymerizable reagents of the photoresist composition. Consequently, the exposed coating portions are rendered less soluble in a developer solution than unexposed portions. For a positive-acting photoresist, exposed portions are rendered more soluble in a developer solution while areas not exposed remain comparatively less developer soluble. Photoresist compositions are described in Deforest, Photoresist Materials and Processes, McGraw Hill Book Company, New York, ch. 2, 1975 and by Moreau, Semiconductor Lithography, Principles, Practices and Materials, Plenum Press, New York, ch. 2 and 4.
More recently, chemically-amplified-type resists have been increasingly employed, particularly for formation of sub-micron images and other high performance applications. Such photoresists may be negative-acting or positive-acting and generally include many crosslinking events (in the case of a negative-acting resist) or deprotection reactions (in the case of a positive-acting resist) per unit of photogenerated acid. In the case of positive chemically-amplified resists, certain cationic photoinitiators have been used to induce cleavage of certain xe2x80x9cblockingxe2x80x9d groups pendant from a photoresist binder, or cleavage of certain groups that comprise a photoresist binder backbone. See, for example, U.S. Pat. Nos. 5,075,199; 4,968,581; 4,883,740; 4,810,613; and 4,491,628, and Canadian Patent Application 2,001,384. Upon cleavage of the blocking group through exposure of a coating layer of such a resist, a polar functional group is formed, e.g., carboxyl or imide, which results in different solubility characteristics in exposed and unexposed areas of the resist coating layer. See also R. D. Allen et al., Proceedings of SPIE, 2724:334-343 (1996); and P. Trefonas et al. Proceedings of the 11th International Conference on Photopolymers (Soc. Of Plastics Engineers), pp 44-58 (Oct. 6, 1997).
While currently available photoresists are suitable for many applications, current resists also can exhibit significant shortcomings, particularly in high performance applications such as formation of highly resolved sub-half micron and sub-quarter micron features.
Consequently, interest has increased in photoresists that can be photoimaged with short wavelength radiation, including exposure radiation of about 250 nm or less, or even about 200 nm or less, such as wavelengths of about 248 nm (provided by KrF laser) or 193 nm (provided by an ArF exposure tool). See European Published Application EP915382A2. Use of such short exposure wavelengths can enable formation of smaller features. Accordingly, a photoresist that yields well-resolved images upon 248 nm or 193 nm exposure could enable formation of extremely small (e.g. sub-0.25 xcexcm) features that respond to constant industry demands for smaller dimension circuit patterns, e.g. to provide greater circuit density and enhanced device performance.
However, many current photoresists are generally designed for imaging at relatively higher wavelengths, such as G-line (436 nm) and I-line (365 nm) are generally unsuitable for imaging at short wavelengths such as sub-200 nm. Even shorter wavelength resists, such as those effective at 248 nm exposures, also are generally unsuitable for sub-200 nm exposures, such as 193 nm imaging.
More specifically, current photoresists can be highly opaque to extremely short exposure wavelengths such as 193 nm, thereby resulting in poorly resolved images.
It thus would be desirable to have new photoresist compositions, particularly resist compositions that can be imaged at short wavelengths such as sub-200 nm exposure wavelengths, particularly 193 nm.
We have now found novel polymers and photoresist compositions that comprise the polymers as a resin binder component. The photoresist compositions of the invention can provide highly resolved relief images upon exposure to extremely short wavelengths, particularly sub-200 nm wavelengths such as 193 nm.
In particular, photoresists that contain preferred polymers of the invention can exhibit significant resistance to plasma etchants. See, for instance, the results set forth in Example 7, which follows.
In a first aspect of the invention, polymers are provided that contain at least three distinct repeat units as follows:
1) a group that include a photoacid-labile moiety, particularly a photoacid-labile group that contains an alicyclic group, e.g. a photoacid-labile ester such as a polymerized alkyl acrylate or alkylmethacrylate preferably where the alkyl group is an alicyclic such as adamantyl, fencyl, and the like;
2) a group that contains a polymerized electron-deficient monomer that is non-photoacid-labile, or at least less reactive (e.g. 2 or 3 times less reactive) to photoacid than units 1), such as an ethylene unsaturated ketone or di-ketone, e.g. an anhydride such as maleic anhydride, itaconic anhydride, citrionic anhydride; amides such as maleimide; esters, particularly lactones; etc.; and
3) a group that includes a polymerized cyclic olefin moiety (i.e. where the olefinic group is polymerized along the polymer backbone to provide a fused carbon alicyclic group).
Without being by theory, it is believed the combined use in polymers of the invention of i) carbon alicyclic groups (provided by polymerization of a cyclic olefin such as a norbornene); and ii) photoacid-labile groups that contain an alicyclic moiety, can impart significantly enhanced resistance to plasma etchants to photoresist that contain such polymers. See the comparative results set forth in Example 7 below. Such etch resistance can be critical to achieve desired results in high performance applications, e.g. forming highly resolved sub-half micron or sub-quarter micron resist features.
Preferred polymers contain at least one additional distinct unit (particularly tetrapolymers or pentapolymers) such as an additional, distinct polymerized cyclic olefin unit. In such tetrapolymers and pentapolymers, suitably at least two distinct polymer units may contain photoacid-acid labile groups. For example, the tetrapolymer or pentapolymer may contain a photoacid-labile acrylate and a cyclic olefin, e.g. a polymerized norbornene, that has a photoacid-labile substituent such as a photoacid-labile ester.
Preferred polymers include those that contain a polymerized first norbornene repeat unit, and a polymerized second norbornene repeat unit, where the second unit is distinct from the first unit. For instance, the first norbornene repeat unit can be unsubstituted, and the second norbornene repeat unit can have one or more non-hydrogen repeat units. Alternatively, the first and second norbornene repeat units each can have one or more non-hydrogen ring substituents, but where the non-hydrogen substituent(s) of the first norbornene repeat unit is different than the non-hydrogen substituent(s) of the second norbornene repeat unit.
The addition of at least two different norbornene monomers enables desired control of lithographic properties of the polymer, particularly with respect to etch resistance, dissolution contrast, adhesion and resolution. For instance, for enhancing adhesion, a first norbornene monomer (e.g. not substituted with any non-hydrogen substitutents) can be polymerized and a second norbornene monomer that has one or more alcohol substituents can be polymerized. For enhanced dissolution control, a first norbornene monomer (e.g. not substituted with any non-hydrogen substitutents) can be polymerized and a second norbornene monomer that has one or more lactone substituents can be polymerized. For enhanced dissolution contrast, a first norbornene monomer (e.g. not substituted with any non-hydrogen substituents, or substituted with other group such as an alcohol or lactone) can be polymerized and a second norbornene monomer that has one or more photoacid-labile substituents can be polymerized.
Thus, in a preferred aspect of the invention, polymers are provided that contain at least two distinct polymerized norbornene repeat units. Preferably such polymers also will contain photoacid-labile groups, either as a substituent of one or both of the two distinct norbornene repeat units, or as a polymer repeat unit separate from the norbornene units. For example, photoacid-labile acrylate units may be present together with the two or more distinct polymerized norbornene repeat units.
In a further aspect of the invention, polymers of the invention are provided that contain at least two distinct units that each have photoacid labile groups. For instance, a polymer may contain an acrylate unit with a photoacid-labile group, and a polymerized norbornene group that has a pendant photoacid-labile group. Alternatively, a polymer of the invention may contain at least two distinct photoacid-labile acrylate units.
In a still further aspect of the invention, polymers of the invention contain a photoacid labile group that contains a tertiary ester alicyclic hydrocarbon group that has two or more fused or bridged rings, and in at least certain aspects of the invention, the alicyclic hydrocarbon group is preferably other than adamantyl. Preferred tertiary ester groups include optionally substituted fencyl groups, particularly ethyl fencyl; optionally substituted pinanyl; and optionally substituted tricyclo decanyl, particularly an alkyl-substituted tricyclo decanyl such as 8-ethyl-8-tricyclodecanyl such as provided by polymerization of 8-ethyl-8-tricyclodecanyl acrylate and 8-ethyl-8-tricyclodecanyl methacrylate. Additional alicyclic ester groups also will be suitable, including additional bicyclic, tricyclic and other polycyclic moieties.
Generally preferred polymers of the invention include those that contain at least one repeat unit that comprises a photoacid-labile group, which contains an alicyclic hydrocarbon moiety. Polymers of the invention also may contain multiple, distinct repeat units, e.g. two distinct repeat units, that each comprise a photoacid-labile group, which contains an alicyclic hydrocarbon moiety.
The invention also includes polymers that contain one or more of the above features. For instance, preferred are terpolymers, tetrapolymers, pentapolymers or other higher order polymers that contain at least the above groups 1) through 3), i.e. 1) (photoacid-labile group); 2) (polymerized electron-deficient monomer); and 3) (polymerized cyclic olefin moiety), preferably where at least two distinct units 1) through 3) each has photoacid labile groups, e.g. the cyclic olefin unit may have a photoacid-labile group. As referred to herein, a cyclic olefin typically refers to a compound that has all carbon ring members (also referred to as a carbon alicyclic). The cyclic olefin will have at least one endocyclic carbon-carbon double bond and will non-aromatic. The endocyclic double bond can serve to polymerize the cyclic group, providing an alicyclic ring fused to the polymer backbone, i.e. two adjacent ring carbons of the cyclic group also are part of the polymer backbone.
Also preferred are terpolymers, tetrapolymers, pentapolymers or other higher order polymers that contain at least the above groups 1) through 3), and where the polymer contains a photoacid labile group that contains a tertiary ester alicyclic hydrocarbon group that has two or more fused or bridged rings, and suitably is other than adamantyl.
Polymers of the invention also may contain units in addition to the above groups. For example, polymers of the invention also may contain nitrile such as provided by polymerization of methacrylonitrile and acrylonitrile. Additional contrast enhancing groups also may be present in polymers of the invention, such as groups provided by polymerization of methacrylic acid, acrylic acid, and such acids protected as photoacid labile esters, e.g. as provided by reaction of ethoxyethyl methacrylate, t-butoxy methacrylate, t-butylmethacrylate and the like.
Polymers of the invention are preferably employed in photoresists imaged at 193 nm, and thus preferably will be substantially free of any phenyl or other aromatic groups. For example, preferred polymers contain less than about 5 mole percent aromatic groups, more preferably less than about 1 or 2 mole percent aromatic groups, more preferably less than about 0.1, 0.02, 0.04 and 0.08 mole percent aromatic groups and still more preferably less than about 0.01 mole percent aromatic groups. Particularly preferred polymers are completely free of aromatic groups. Aromatic groups can be highly absorbing of sub-200 nm radiation and thus are undesirable for polymers used in photoresists imaged with such short wavelength radiation.
The invention also provides methods for forming relief images, including methods for forming a highly resolved relief image such as a pattern of lines where each line has essentially vertical sidewalls and a line width of about 0.40 microns or less, and even a width of about 0.25, 0.20 or 0.16 microns or less. The invention further provides articles of manufacture comprising substrates such as a microelectronic wafer substrate or liquid crystal display or other flat panel display substrate having coated thereon a polymer, photoresist or resist relief image of the invention.
In a still further aspect, the invention includes novel compounds that are useful to prepare polymers of the invention. In particular, 8-alkyl-8-tricyclodecanyl acrylate and 8-alkyl-8-tricyclodecanyl methacrylate are provided, together with methods of synthesis of those monomers.
Other aspects of the invention are disclosed infra.